Among fatty acids included in bovine intramuscular fat, the most abundant one is mono unsaturated fatty acid with 18 carbon atoms (oleic acid). In particular, the beef of Japanese Black breed has been reported as one containing a significantly high amount of oleic acid compared with that of the foreign breed (see Non-patent Document 1). In general, it is said that the beef of Japanese Black breed has an excellent Japanese-preferred eating quality compared with that of the foreign breed. As one of its factors, it may be due to rich oleic acid content in Japanese Black cattle beef in comparison with that of the foreign breed (see Non-patent Document 2).
In order to determine beef fatty acid composition, including oleic acid, large experimental arrangement such as a draft is required, and technical skills are also indispensable for obtaining correct data. Further, there are many other problems such that: it is difficult to process a lot of samples at a time because it takes a long time for the determination; and a large amount of an organic solvent is used in a stage of fatty acid extraction or the like, so the harmful effects of the organic solvent on the health of a person who carries out such a determination cannot be ignored.
On the other hand, currently, the breeding of the beef cattle in Japan is carried out on the basis of the carcass grade determined by the Japan Meat Grading Association.
However, as described above, complicated physiochemical analyses must be required for determining the feature of the fatty acid composition or the like that is associated with the eating-quality of beef. Thus, unlike the carcass grade, the data cannot be easily obtained. Therefore, the feature has not been considered as target traits for improvement till now. As far as such a situation persists, it is probable that the chance of adopting the above feature as the target traits for improvement is low in the future.
Therefore, it has been demanded to develop a method of determining the fatty acid composition of beef on the basis of a genetic base sequence, which can be carried out by a simple device without much need of technical skill.
Heretofore, a technology for evaluating the eating quality of beef by determining the melting point of fat and the unsaturated degree of fatty acid in beef using the genotype of stearoyl-CoA desaturase (SCD) has been already patented (Patent Document 1).
The determination of the eating quality of beef using the SCD gene, which is described in Patent Document 1, is carried out on the basis of the relationship between the eating quality and the melting point of fat in the beef and the relationship between the eating quality and the unsaturated degree of the fatty acid in the beef. In this case, the unsaturated degree of the fatty acid composition is calculated from the ratio of the total content of saturated fatty acids to the total content of mono unsaturated fatty acids in the fatty acids of beef, so it is impossible to obtain the amount of fatty acid separately by every kind thereof.
Fatty acid synthase (FASN) gene is known as an enzyme for fatty acid synthesis in the bovine muscle. The enzyme is one of the enzymes responsible for in vivo fatty acid synthesis. The entire gene sequence from the cattle (Bos taurus) and the amino acid sequence estimated therefrom are described in Non-patent Document 3 listed below.
However, any method of determining fatty acid composition on the basis of the genotype of fatty acid synthase has not been known.    Non-patent Document 1: May S. G. et al., Comparison of sensory characteristics and fatty acid composition between Wagyu crossbred and Angus steers, Meat Science 35, 289-298 (1993)    Non-patent Document 2: Matsubara et al., Quality of and Consumer Preference for Marketing Beef, Bull. Hyogo Pre. Agri. Inst. (Animal Husbandry) 34, 10-15 (1998)    Non-patent Document 3: DDBJ/EMBL/GenBank databases: Accession Number AF285607    Patent Document 1: JP 2004-261014 A